This project has been designed to investigate the regulation of vasomotor responses in the mesenteric and hindlimb vascular beds of dogs by autonomic nerve fibers, and in particular to determine the role of such nerves in vasodilator responses. Experiments are carried out in anesthetized dogs. Measuring mesenteric and hindlimb blood flows with electromagnetic flowmeters during direct stimulation of nerves, and during close intra-arterial injection of drugs. Among the drugs under study are acetyl choline and dimethyl phenyl piperazinium (DMPP), both of which appear to be able to release neurotransmitters from the terminals of autonomic nerve fibers. Blood flow responses to chemical and electrical stimulation of autonomic nerves will be measured before and after administration of a number of autonomic blocking drugs, and before chemical and surgical denervation of the mesenteric and hindlimb vascular beds. In this way, it should be possible to define more clearly the role, if any of vasodilator nerves to these vascular regions, as well other factors, such as contraction of intestinal smooth muscle or hindlimb skeletal muscle, and reactive hyperemia following vasoconstrictor responses, also will be among the aspects to be studied.